Chesapeake losing its oyster reefs faster than they can be rebuilt
There aren’t enough shells to go around for wild fishery, aquaculture and sanctuaries
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The Chesapeake Bay has an oyster problem — but more fundamentally, it has a shell problem.
Put simply, there aren’t enough oyster shells available to support a large-scale restoration of the Bay’s depleted bivalve population. And the way things are going, there may not even be enough to sustain the wild fishery a whole lot longer, at least in Virginia.
Decades of overharvesting, habitat destruction, disease and poor water quality have reduced the population of oysters in the Bay to less than 1 percent of its historic levels. And in much of the Bay, oyster reefs — made up of the shells of living and dead bivalves — are wearing down and disappearing faster than they’re being built up.
Scientists, managers and others worry that there aren’t enough shells to go around to sustain the traditional wild fishery as well as a growing aquaculture industry, not to mention ambitious large-scale efforts by both states and the federal government to restore the Chesapeake’s oyster population for its ecological value.
“We don’t have the habitat,” said Bruce Vogt, manager of ecosystem science and habitat assessment for the National Oceanic and Atmospheric Administration Chesapeake Bay Office. “Even if we had adequate spawning stock to revive the population over time, the habitat just isn’t there.”
It’s the classic chicken-or-egg dilemma. Oysters make their own habitat, building reefs out of the shells they produce. But juvenile oysters need a hard surface — customarily, another oyster shell — on which to grow. The problem now is that there are many fewer shells than there used to be on which the shellfish can live and reproduce.
The losses stem from a variety of factors. In the last century, as much as 70 percent of the 450,000 acres of oyster reef habitat that once blanketed the bottom of the Bay and its tributaries has been lost to siltation, according to an environmental assessment done in 2009 by the U.S. Army Corps of Engineers. Reefs have been smothered by a deluge of silt washing off the land, which has yet to let up.
Oyster shells are being lost in other ways, too. Their shells are broken up by predators, such as cownose rays, black drum, crabs, boring sponges and shell-boring snails known as oyster drills. Shells are removed by harvesting, too, and not always returned; and the gear used to dredge up oysters scatters and breaks other shells.
Finally, perhaps most significantly of all, the shells themselves dissolve naturally over time. While oysters are alive, they keep producing new shell from carbon and calcium that they filter out of the water. But after the bivalves die, dissolution takes over; the shells begin to corrode. One study estimated shell loss ranging from 2 percent to 70 percent per year, depending on water conditions. The saltier or more acidic the water, the faster the process.
To better understand the challenge, the state-federal Chesapeake Bay Program is commissioning a “shell budget” — an analysis of how many oyster shells are being lost and how many produced by new oysters. The study, estimated to cost $50,000–$60,000, is expected to be completed in about a year.
“We really need to put all this together,” said Peyton Robertson, director of NOAA’s Bay office and co-chair of the Bay Program’s Sustainable Fisheries Goal Implementation Team. “We don’t have a good handle on the puts and takes of shell coming in and going out.”
Large reefs of the past
Shells coming in start with spat, tiny free-swimming baby oysters that settle to the bottom. There, they attach themselves to the shells of mature oysters, or to the empty shells of animals that have died. As the spat grow, they create and expand their shells, building oyster reefs in generational layers of shells.
“There were times when big oyster reefs were sustained in the Bay,” recalled Mark Luckenbach, a Virginia Institute of Marine Science researcher who’s studied oyster reef ecology. When Capt. John Smith explored the Chesapeake in the early 1600s, he reported that oysters “lay as thick as stones” on the bottom. A century later, a visitor arriving by ship remarked on the oysters’ incredible abundance, noting that “whole banks” of them posed navigational hazards.
That bounty helped to feed a growing nation, and Chesapeake oysters harvested from those reefs were shipped across the country to feed a seemingly insatiable demand. Harvests peaked in the 1880s, with a phenomenal yield of 17 million bushels in a single year.
After that, the catch began a gradual, ragged decline and nearly collapsed in the early 2000s as a pair of diseases ravaged the remaining shellfish. The diseases have abated some since then, and a couple of good years of natural oyster reproduction enabled the wild fishery to make a partial comeback. But it remains a shadow of what it once was, with around 2,000 licensed harvesters in both states pulling up a combined one million bushels. Scientists and some fishery managers worry that even that is unsustainable, given the vastly reduced reef habitat.
“It took you 10,000 years to build oysters reefs in the Bay, and it took a few hundred years to disassemble them,” said Roger Mann, a veteran oyster researcher at the Virginia Institute of Marine Science, who with other scientists has published several papers on shell budgets.
“Once these reef systems have effectively gone away or gotten buried,” he added, “you can’t easily replace them.”
When oysters were more abundant, no one bothered returning the shells of harvested bivalves to the water. Many were ground up and used to build roads and driveways, among other things. Now, with recognition of their worth, much of what’s harvested gets recycled. Oyster-packing houses sell the shells from oysters they shuck to aquaculture operations, or to hatcheries for use in producing new generations of bivalves. Many restaurants and seafood businesses have joined in the effort to conserve and reuse shells that used to be thrown away. But recycling is not enough to offset all of the lost shell needed to supply a growing aquaculture industry and enable the rebuilding of reefs that were worn down or buried long ago.
Fossil shells & recycling
For years, managers looking to maintain wild harvests have made up for the lack of adequate natural shell production on reefs by supplementing them with the limited supply of recycled fresh shells and with fossil shells, dredged up from the bottom of the Bay and its rivers.
The Virginia Marine Resources Commission gets about $2 million a year for re-shelling its public oyster reefs. Jim Wesson, the VMRC’s chief of oyster conservation and replenishment, said the funds go to dredging a fossil shell deposit in the James River. They’re put down on reefs where the VMRC’s patent-tong surveys show the layer of oysters and old shell has grown too sparse or thin to get a good crop of new oyster recruits.
“We are always losing shell,” Wesson told members of Maryland’s Oyster Advisory Commission last fall, “and if we don’t put shell back, then we cannot maintain any stability in our oyster beds, and we’ll lose them all.”
The expenditure has been a good investment, Wesson said, with the wild harvest earning $5–$7 in dockside value for every dollar spent on the fossil shell.
But even though the Virginia General Assembly increased funding for the shell restocking several years ago, it’s not enough to cover all of the reefs that need it, Wesson said. The James River dredging operation has been yielding about 500,000 bushels’ worth of fossil shells, he said, but to ensure good spat set on reefs, the shell density must be about 1,000 bushels per acre.
“You’re only talking about doing 500 acres a year,” he said an interview. But the latest surveys, he added, “say well over 1,000 acres need new shell.”
Increased funding would allow more fossil shell to be dredged, Wesson said, but the James River deposit being worked is the last big shell reservoir he knows about. Wesson said he doesn’t know for sure how long this supply will last, as it hasn’t been surveyed. But he figures that at current removal rates, there may be enough fossil shell left to last a couple of decades at most, and maybe much less.
Maryland used to dredge even more fossil shells from buried deposits in its end of the Bay for use in replenishing its public fishery reefs.
“We planted 5 million bushels (of shells) per year,” recalled Chris Judy, shellfish program manager for the Department of Natural Resources.
For a time, those plantings more than offset what was being lost through harvesting, he said. Shells don’t dissolve as rapidly in the less saline waters in the Upper Bay, Judy pointed out, and there aren’t as many boring organisms to break them up. The DNR’s reef surveys can still find intact shells that were planted 20 years ago, Judy said.
But siltation is a much bigger problem in the Upper Bay, as shells get smothered by fine sediment settling out of the water or sinking into the soft muddy bottom. And there’s no question that much reef habitat has been lost in Maryland waters as well. As just one indicator, the DNR’s annual fall survey of reefs has found it takes longer to fill the dredge with shell than it used to, Judy said.
Maryland stopped dredging fossil shell in 2006, and until recently has not seriously pursued that avenue. State officials decided years ago to shift resources away from maintaining the public fishery while encouraging the development of an aquaculture industry like Virginia has.
In the last several years, as part of the Bay restoration effort, both Maryland and Virginia have committed both to restoring oysters for their ecological value as water filterers and to rebuilding their reefs because they provide habitat for many other fish and marine creatures. The two states pledged to conduct large-scale restoration efforts in five Bay tributaries each.
But with the restoration projects calling for the creation and enhancement of hundreds of acres of reefs — potentially requiring millions of bushels of shells each — state and federal agencies have had to be creative. Getting oyster shells from Louisiana proved too expensive, so they have resorted to building reefs with granite rocks and clam shells. Maryland even contracted at one point to buy fossil shells dredged from a quarry in the Florida panhandle.
Natural oyster shell is generally considered the best material on which to raise new oysters, but there’s ample evidence that spat will settle and grow on almost any hard surface. Preliminary results of a DNR survey last fall found the highest spat density anywhere in state waters on a reef in the Little Choptank River built with the Florida fossil material. Watermen have objected, though, to using anything but oyster shells in restoration projects, citing complaints about water quality with the Florida material and interference with crabbing rigs around rock reefs. They have succeeded in blocking or at least reducing any further use of those materials.
Now, the Maryland DNR is seeking to tap one of the Bay’s largest remaining fossil shell deposits — Man O’War Shoal, near the mouth of the Patapsco River. The state has applied for a federal permit to remove 5 million bushels of shells from the massive underwater mound, which by some estimates holds 90 million–100 million bushels in all.
But dredging there is opposed by many conservationists, recreational anglers and even some commercial fishers, who say the reef, though it now harbors few live oysters, is a vital breeding ground and habitat for striped bass and other fish.
The Baltimore District of the Army Corps of Engineers, which decides on such permits, has been studying the state’s dredging request for more than a year and has asked repeatedly for more information. The DNR intends to respond soon to the Corps’ latest round of queries and hopes to get a decision by this spring, Judy said.
Even if the dredging is permitted, Judy said, that 5 million bushels won’t be enough to satisfy all of the demand in the state for shells. The DNR estimated that to sustain the wild fishery, supply the state’s growing aquaculture industry and help rebuild reefs for the restoration effort would require 11 million bushels. And that’s just the projected need for the next five years.
“Shells are crucial,” Judy said, and “maintaining the shell habitat is important for industry, restoration and aquaculture. But what’s available at Man O’War is just a small amount of what’s needed.”
Where to get, put the shell
Mann, who expects to work with Wesson on the shell budget study, said he hoped that by analyzing data from reef surveys conducted over the last 20–30 years in Maryland and Virginia, they can map a clearer picture where reefs may be holding their own and where they are disappearing.
Their report is due in a year. Once the budget is laid out, Mann said, “you end up with some fairly harsh decisions [to make]. Then the question is, if you’re going to focus on restoration and maintenance of the fishery, where do you get the shell, where do you do the restocking?”
And that, he added, is “going to be, I think, fairly sobering.”
Because harvesting impacts reefs, Mann said, some will wonder what percentage of oysters need to be left behind to maintain the shell base.
“It turns out that number is quite substantial,” he said. There are reefs in the James River with stable oyster populations that don’t get restocked with shell. From those reefs, he said, “we’re probably taking 6–8 percent of the oysters.”
Conservationists argue for reducing the harvest, or at least for creating and maintaining large sanctuaries. But Wesson cautions that under current conditions, at least, simply leaving oysters alone may not be the answer. Reefs in Virginia’s oyster sanctuaries are losing ground and need replenishment, he said just like neighboring reefs that get worked over regularly.
VIMS’ Luckenbach called it a “vicious cycle,” that the Bay’s sparse oyster population can’t hold its own, much less rebuild. “It isn’t really fixable,” he added, “without biting the bullet and working really hard to get to higher population levels.”
Even so, he and others say, restoration is likely to take decades of work, with repeated applications of shell, before oysters can become plentiful enough again to make reefs self-sustainable.
Meanwhile, Mann said, the realities of the shell budget will confront policy makers with some tough choices. Without enough shell for all the needs, do they stop using it to prop up the public fishery and push watermen into oyster farming?
“If you have people who’ve made a living this way for all of their life, are you going to be telling them they need to be opening new businesses?” he asked.
Or, given the massive supply of shell that might be needed to rebuild lost reef habitat, Mann asked, should policy makers rethink the goal, or at least the pace of their large-scale restoration efforts?
NOAA’s Robertson acknowledgedthe difficulty of the decision, but sees it differently.
“If we put all our eggs in the basket of doing the wild fishery for another decade, we’re just forestalling what we’re going to face,” Robertson said. “That’s not going to bring them back; it just brings up this longer-term quandary. What are we going to do? Are we trying to sustain a short-term fishery or to bring back the oyster population?”
And now, the states’ ability for the near term to keep going after fossil shell in the Bay may be in jeopardy. The specially outfitted hydraulic dredge that’s been used to recover the James River fossil shell is now for sale. Jim Matters, its owner, said he’s retiring.
With only the Virginia shell dredging contract right now, Matters said, “there’s not a lot of work for the machine.” It can be used for other purposes, he noted, such as maintaining navigational channels. But then the shell-processing equipment that he’s added would no longer be needed.
Wesson said that if Maryland did get Corps approval to dredge Man O’War Shoal, that, along with the Virginia work, might enhance prospects for someone to buy the dredge and keep it working on excavating shell from the Bay.
But if the dredge is sold and moved, Virginia suddenly loses that supply, and it’s not clear how Maryland would hope to get the shell it wants. DNR’s Judy declined to comment on that prospect, saying, “You’re stating the obvious.”
Wesson said he’s working “as hard as I can” to find someone willing to buy the dredge and keep it digging up fossil shell in the Bay. He said he’s cautiously optimistic. But If it gets bought and taken elsewhere, he warns that the curtain may fall on the wild harvest of bivalves in Virginia, and eventually in Maryland as well.
“If we don’t have it, we’re both done,” Wesson said.
- Category: Fisheries
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